Computer Aided Design (CAD) systems are used to design and simulate virtual models of electrical, electronic or mechanical devices prior to producing actual physical devices. CAD systems are interactive software tools that run on a digital computer with a graphical display device. In particular, micro-fabricated devices such as electronic integrated circuits (ICs) and Micro Electro-Mechanical Systems (MEMS) can be designed and simulated virtually using CAD systems prior to beginning the costly and time-consuming process of fabricating the actual physical devices.
MEMS are micro- or nano-scale devices typically fabricated in a similar fashion as integrated circuits (ICs) to exploit the miniaturization, integration, and batch processing attainable with semiconductor manufacturing processes. Unlike ICs which consist solely of electrical components, MEMS devices combine components from multiple physical domains and may contain, for example, electrical, mechanical, and fluidic components. MEMS devices appear in many forms and may include micro-electromechanical sensors and actuators such as gyroscopes, accelerometers, and pressure sensors, micro-fluidic devices such as ink jet heads, Radio-Frequency (RF) devices such as switches, resonators, varactors, and passives, and optical devices such as micro-mirrors and fiber alignment devices.
The behavior of both MEMS and IC devices can be modeled at the system level as an interconnected network of simpler components. Each component has an underlying mathematical description, or behavioral model, which is referred to herein as a component model. Typically, these component models are parameterized, i.e. they take as input a few parameters such as width and height, so that the same mathematical model can be used for different versions of the same type of component. For example, a single component model may be used to generate particular models having different dimensions. A system simulator numerically computes, or simulates, the collective behavior of the network of component models.
Two commonly used methods of implementing a system simulation are circuit simulation (also referred to as conservative system simulation) and signal-flow simulation. A system model is captured graphically in a circuit schematic or in a signal-flow diagram, and then its behavior is simulated by, respectively, a circuit simulator or a signal-flow simulator. Traditionally, circuit simulation has been used for electronic circuit design while signal-flow simulation has been used for control system and signal processing design. Currently, both types of system simulation are used to simulate not only ICs, but also multi-physics devices such as MEMS.
Since MEMS devices can also be simulated by system modeling methods such as circuit simulation, CAD systems for IC design can be applied to MEMS design, at least in principle. In particular, IC schematic editors and circuit simulators may be applied to MEMS design when supplied with a library of MEMS component models such as mechanical beams, plates, electrodes, magnetic coils, optical lenses and lasers. Unfortunately, there are a number of drawbacks to the application of CAD systems originally intended for IC design to the MEMS design process. Schematics representing MEMS are usually rather abstract representations of 3D objects in space. The geometry, position and orientation of each modeled substructure is defined by the parameters of the corresponding schematic symbol. Minor parameter changes can result in substantially different device geometry and/or optical system setups. While conventional IC design tools allow the user to extract a two-dimensional layout from a schematic, they do not include the 3D visualization capability needed to understand and verify the parameter settings and symbol connectivity of non-electrical structures like MEMS.
Additionally, conventional methods of visualizing schematic designs of a model make it difficult to interpret network simulation results. Unlike conventional IC system modeling environments, working efficiently with MEMS models requires a 3D graphical environment for visualizing the shape, orientation and position of the modeled structures. In conventional IC schematics, electrical “wires” connect the schematic symbols. The results of circuit simulations, such as voltage and current changes over time or frequency on individual wires, can be displayed graphically in 2D “X-Y plots”. Two-dimensional X-Y plots are generally sufficient for understanding purely electrical circuits. MEMS simulations, however, involve spatial displacements and/or rotations of the mechanical substructures or other physical entities such as beams of light. The symbols that represent the MEMS components or substructures are linked by mechanical “wires” that are associated with mechanical degrees of freedom, such as spatial displacements, rotations, forces, or torques. The wires in a MEMS schematic may also be optical “wires” that represent properties of light beams, such as the light intensity within a frequency band. Similar to simulations of electrical circuits, these non-electrical quantities from MEMS simulations can be displayed in X-Y plots. For example, the displacement of a beam component along the x-axis versus voltage change at an electrode can be shown in an X-Y plot. These X-Y plots are not sufficient, however, for understanding the motion of a complex MEMS that may consist of tens or hundreds of individual mechanical components and/or multiple optical beams.